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Electricity & Magnetism

Electricity & Magnetism. Universal Forces Throughout all galaxies far, far away………. Remember, FORCES exert a push or pull on objects and can do WORK They can act over a distance without touching Gravitational force – a weak force due to mass

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Electricity & Magnetism

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  1. Electricity & Magnetism

  2. Universal ForcesThroughout all galaxies far, far away……… • Remember, FORCES exert a push or pull on objects and can do WORK • They can act over a distance without touching • Gravitational force – a weak force due to mass • Electromagnetic force – a stronger force due to charged particles • ELECTRICITY • MAGNETISM

  3. What is a charge? • All matter is made up of atoms • All atoms are made up of : • Protons (+) • Neutron ( 0) • Electrons (-) • Electrons extremely SMALL mass • travels extremely FAST • has A LOT of KINETIC energy !

  4. What is a charge? • Atoms are normally NEUTRAL because: # of PROTONS = # of ELECTRONS • Electrons can move easily between objects • When an object LOSES electrons  positively charged # of PROTONS > # of ELECTRONS • When an object GAINS electrons  negatively charged # of PROTONS < # of ELECTRONS • This movement of electrons can transfer energy and do WORK.

  5. Check for UnderstandingWhat would occur to make a positive or negative particle? + - - + + + - - + + - - - NEGATIVE POSITIVE

  6. Law of Charges • Like charges REPEL or PUSH (+ and +) OR ( - and -) • Unlike charges ATTRACT or PULL (+ and - ) • FORCE is exerted by electric charges!

  7. Check for Understanding:Would the following repel or attract each other? • REPEL • ATTRACT • REPEL - - and - + and + + and

  8. Electrons (-) push each other away • Electrons (-) are pulled toward protons (+) or other positively charged objects

  9. Induction • Some objects that really have an equal amount of charges, can temporarily shift their electrons so that an area may become more positive or negatively charged.

  10. Static Electricity • Charges that build up is called static electricity. • Pollution control systems to capture smoke particles • Photocopiers, speakers, microphones • Lightning • Muscle cells • However, in general, static electricity is a nuisance! • Van der Graaf and Rockin’ Bill Nye

  11. Static discharge • Discharge is a sudden movement of electrons • Unpredictable • Unreliable • Its just not really useful. • Static discharge occurs when a new path forms between two areas of opposite charge. • The electrons move suddenly to try to restore the balance between charged areas.

  12. Pair Share:How would you explain getting “shocked” by the doorknob?

  13. Electric Current • Static discharge is brief and limited in the number of electrons it moves. • To do USEFUL WORK, we need a continuous flow of charge. • This is an electric current.

  14. Electric Current, Cont. • For an Electric Current, we need… • A steady supply of moving electrons • A path for the electrons to follow and return to be reused. • Something to “push” the electrons along the path.

  15. Water Analogy • Water in a high reservoir (PE) causes a downward force through pipes to a lower reservoir. • The higher the reservoir, the higher the PE. • Water flows through pipes in a continuous path. Higher reservoir creates flow with more KE. • Water is pumped back up to the higher reservoir to be re-used.

  16. The electric circuit… • Electrons “flow” along a closed path with no breaks. • Battery chemicals provide the “push” of electrons, acting as a “pump”. (ELECTRICAL FORCE ) • The “strength” of the battery provides the PE of the circuit. Work is done as electrons flow through a circuit .

  17. Circuit Construction • pHet Circuit Construction interactive

  18. Let’s talk numbers! • A battery is a device that converts chemical energy to electrical energy. • In a battery , one terminal (end) is Positive and the other terminal (end) is Negative. • The PE of the electrical flow of electrons from one end to the other is the voltage of the battery. • Higher voltage = Higher “push” of electrons through the circuit (Joules/Coulomb)

  19. Let’s talk numbers! • Coulomb (C) • Is a bunch of electrons (6.25X 1018 electrons) 6,250,000,000,000,000,000 electrons • 1 Volt is the PE that can move 1 Coulomb of charge using 1 Joule of energy • Ampere(amps) is 1 Coulomb in one second ( C / s)

  20. What if we add…a water wheel ? • A wheel would hinder the flow – like friction. • Water uses some of it’s energy to make the wheel turn (work) • Water flows on through the wheel to continue the flow. • More than one wheel could be put into the flow of water.

  21. Resistors • Resistor = any object or substance that slows down the flow of electrons. • Electrons transfersome of their Kinetic energy when going through a resistor, so this is a place of energy conversion: • Light bulb  light energy • Heating element  thermal energy • Speaker  sound energy • Resistance measured in ohms. (Ω)

  22. A short circuit: • Resistors also protect a circuit from becoming a SHORT CIRCUIT! • Too much current!! • Wires get HOT! • Plastic covering can melt. • Fire may start. • Drains battery fast – or flips protective circuit breakerin electrical panel.

  23. Stop Here

  24. Magnetism • Early discovery of natural occurring lodestones • they always oriented themselves north when floated on a piece of wood on water and • they concentrated iron shavings • There are Naturally occurring magnets and Man-made magnets. • Current science understands magnets to ALWAYS have a NORTH and a SOUTH pole, no matter how many times you divide a magnet(Di-Pole)

  25. Effects of Magnetism • Magnetic fields show the strength and direction of magnetic forces. • Closer lines = more strength • Force lines point from north pole to south pole • Same poles REPEL • Opposite poles ATTRACT • Effects of magnetism is very similar to the effects of static electrical charges.

  26. Magnetism from Electricity • Magnets attract only a small group of materials. • Iron, nickel, cobalt, steel • We can INDUCE magnetism in some materials, especially iron. • A wire carrying a current that is coiled around a metal core strengthens the magnetic field. • The more coils, the STRONGER the magnetic field (lab!) • Electromagnets = magnets created by use of electric current. Li nk

  27. Electricity from Magnetism • Does this work the other way around? • YES! If a magnet is moved through a coil of wire, a current is produced in the wire. • pHet Faraday interactive

  28. What did you notice about the current flow? • The current only flows when the magnet is moving! When the magnet stops moving, so does the current. • The magnet PULLS the electrons along through the wire. • The more quickly the magnet moves, the faster the electrons move, SO….more current. • Remember… current is more electrons per second • More work is being done!

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